How much difference in compression would changing from 64 cc heads on a 350 to 72cc heads with flat top pistons. Im assuming going to the 72's you would have to change to dome pistons.

I was just wondering about compression loss.

 

WAG but i'd say you'd lose a point for sure, have to do the math to know exactly what it'd be.

 

64cc will give you around 10.3:1 with typical gaskets & block clearance. 72 cc will give you around 9.7:1 with the same parts.

Minimal difference, really; 2-3% of the HP.

I would not put domed pistons in any motor I expected to run on modern pump gas. The HP from the miniscule increase in CR would be more than cancelled out by the poorer flame travel, increased tendency to detonate (requiring significantly reduced timing), etc.

People tend to put too much emphasis on having the highest possible CR, without understanding the sacrifices that sometimes have to be made to get it. In many cases the cure is worse than the disease.

What are you really asking?

 

Well, I plan on leaving the bottom end of my 350 TPI stock except for a cam, Some head manufactures produce 58, 64, 68, 72, 74cc heads. I was just wanting to know which cc head would be best with the stock pistons. Which I may change to a 383 with flat tops later on. I dont want to have to mill the heads, but dont want too much compression to run pump gas.

Im looking at the 64cc maybe aluminum. I know that it makes a difference about the pump gas depending on the compression and if it is a iron or aluminum heads.

Im just trying to get a good combo. I dont want AFR heads. I just want to be different, And Im not sure about going aluminum.

If I can get a iron head that will flow good numbers, have decent compression and at a good price, I would go with iron.

I know that aluminum can warp if the engine gets hot enough.

Just dont know which way to go.

thanks for any advice you can give me.

 

I would wait to make for sure your going to do the 383 or not. Both internal motors vary alot.
On a 383, you can have awesome torque without the needed high compression. And 383 pistons are not available in alot of compression ratios. So you choices will be limited.
If you do a 383, cam will also play an important role on selection for compression. Some cams work with higher compression, so actual help boost. So it really will depend.
I have the iron 64cc heads on my 383, and I have 10.7:1 compression, and around 8.34 DCR. So the cam had to play an important role as well, to help bleed off some cylinder pressure.
If I were you, the 72cc heads will be fine, and you won't need the tricky timing curves, and 93 octane gas like mine does.

Hope this helps....

 

If I go with just a 355 and flat top pistons, will the 64cc be ok?

Im not sure about the 383, but a 355 with the stealth ram and a good cam with the right heads, headers, suspension, and stall converter sounds good to me.

I just need to pick the right heads. I dont have to go radical, but I do want to change the top end, and maybe rebuild the bottom end later.

thanks for any advice anyone can give me.


hey polecat, what kind of times are you getting with that setup.
I wll be running 3.73's, how do you like the 411's

 

Sorry, should have mentioned, this 383 is in my daily driver truck. 4120 lbs. and runs 13.40's now. Adding 150hp shot, should be 12.40's.
But in a car, it should be low to mid 12's.


The 64cc heads may be your ticket.

 

polecat

Do you like your sportsman II heads. I was thinking about going with them.

I wanted to find out how everyone likes them.

 

Trust me here, get the Dart Iron Eagles over the Sportsman II's...after I bought mine, about 9 months later they started using oil, and had to have new bronze guides put in, performance valve job, new seals, etc at a tune of $400 to fix the factory flaws. I have heard many have encountered this problem.
The Darts flow better out of the box than SPII's, and come with bronze guides as well.

 

I was also thinking about the trickflows 23* heads. What have you heard about them?

 

I talked to tons of guys that hate the trickflows. Why dont you look into the dart pro 1 aluminum heads. I just put this combo together in my sig. The engine will be done next week. It dynos at 580 HP and 523 LB TQ on Desktop Dyno2000.

 

Why would you replace pistons to maintain the cr on a 350
that "you want to keep the stock bottom end" for heads you would buy for a planned ,383. Why not just build the 383.

Give your head a shake.

Use 64 cc heads for both motors. Just buy the right D-dish pistons for the 383 when you get to it. So you can bolt on the new 64 cc heads.

You could just port your own TPI heads. If they are 083 castings
they should perform pretty good when ported.

Do a thorough job and you won't need new heads or a 383.

 

I think I will get the Dart Iron Eagle heads " bare castings". Then I will put the springs, valves, retainers, locks, and roller rockers that will suit the cam I buy. I found a guy that does real good head work, and from what I have found out that most engine builders wont buy assembled heads. They were built on a assembly line, and who knows what kind of springs and valves they really have.

I think I will do a stock bore for now maybe a 355 later, 200cc Dart Iron eagle heads, cam, headers, and Port and siamese the intake. Add a 3500 stall, transgo kit, 3.73 gears, and BFG drag radials. This should pick my car up pretty good.

Im going to do this in stages, so I will have time slips to post for which mod I do.

thanks guys